In a virtualized environment with PCI devices passed-through, disabling and enabling decoding is not trivial, and in some configurations can take up to 2 seconds of wall clock time to complete. Since this operation could be done once around each device for devices with multiple BARs (reducing redundancy), add an additional decode disable/enable mask at the device level to prevent redundant disable/enables from occurring during each BAR sizing operation, when pci_read_bases() is the originator. Since __pci_read_base() can also be called independently, keep the current disable/enable mask in that function as-is. Since printk cannot be used while decoding is disabled, move the debug prints in __pci_read_base() to a separate function, __pci_print_bar_status(). To enable this, add pointers to the signature for __pci_read_base() through which the caller can access necessary data from __pci_read_base() and pass it to __pci_print_bar_status(). This has been tested on an SR670v2 host and guest VM, a DGX H100 host and guest VM, and a DGX A100 host and guest VM. I confirmed that BAR info logged to dmesg was consistent on each between unmodified 6.12.1 and with this patch, that BAR mappings in /proc/iomem were consistent between versions, and that lspci -vv results were consistent between versions. On the A100/H100, I also confirmed that the Nvidia driver loads as expected with the patch, and that VM boot time with cold-plugged, passed-through GPUs is about 2x faster. No regressions were observed. Originally developed/tested against upstream 6.12.1, but I also confirmed that this applies cleanly to the pci tree @ v6.13-rc1 and that it results in the same boot speed decrease there when tested in an H100 guest VM. Link: https://lore.kernel.org/all/CAHTA-uYp07FgM6T1OZQKqAdSA5JrZo0ReNEyZgQZub4mDRrV5w@xxxxxxxxxxxxxx/ Reported-by: "Mitchell Augustin" <mitchell.augustin@xxxxxxxxxxxxx> Closes: https://lore.kernel.org/all/CAHTA-uYp07FgM6T1OZQKqAdSA5JrZo0ReNEyZgQZub4mDRrV5w@xxxxxxxxxxxxxx/ Mitchell Augustin (1): PCI: Add decode disable/enable to device level and separate BAR info logging into separate function drivers/pci/iov.c | 16 ++++- drivers/pci/pci.h | 7 ++- drivers/pci/probe.c | 149 +++++++++++++++++++++++++++++++++++++++++--- 3 files changed, 158 insertions(+), 14 deletions(-) --- base-commit: d390303b28dabbb91b2d32016a4f72da478733b9 -- 2.43.0
